Customs spokesman Leon Beddington did not identify the suspect, but correspondents believe he is a coach for the Uzbek team.
Officers stopped a member of the Uzbekistan Olympic delegation at Sydney airport during what was described as a targeted search.
A spokesman said it was believed that at least two vials of human-growth hormone (HGH) had been found in his luggage.
There is no reliable test for identifying abnormal use of the muscle-building substance but labels on the vials carried the name of the substance.
Customs spokesman Leon Beddington did not identify the suspect, but correspondents believe he is a coach for the Uzbek team.
Mr Beddington said the suspect had not been arrested or detained and was co-operating with the authorities.
Uzbek radio reported that 77 track and field athletes and their coaches left the capital, Tashkent, on Wednesday.
International co-operation
The Vice-President of the International Olympic Committee (IOC), Dick Pound, described the alleged attempt to bring in the growth substance as reckless.
"You have got to be nuts, with all the publicity on cracking down on drug use in the Games, to come whistling through customs with HGH," he said.
But he said the seizure highlighted the success of heightened co-operation between the IOC and national governments in cracking down on drug abuse in sport.
Australian Olympic Committee Secretary-General Craig Mclatchey said the AOC, with IOC help, had introduced "the most comprehensive anti-doping framework" in Olympic history.
Crackdown
In March, Australia passed a law setting the penalty for importing "commercial quantities" of HGH without permission at up to five years in prison and/or a heavy fine.
Australian Sports Drug Agency officials have already started testing athletes as they arrive in Australia.
They hope to test 400 athletes for the banned drug EPO, or erythropoietin - which boosts the production of oxyen carrying red blood cells - before the Games start on 15 September.
On Wednesday, China withdrew 27 athletes from its team, some of whom had tested positive for banned substances.
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